DELAY AND QUADRIPARTITION IN SEA URCHIN EGGS INDUCED BY SHORT EXPOSURE TO 2-MERCAPTOETHANOL

¹ Department of Radiology and Department of Biology, Case Western Reserve University, Cleveland, Ohio and Marine Biological Laboratory, Woods Hole, Massachusetts

Eggs of Arbacia punctulata and Lytechinus variegatus were treated with 0.1 M 2-mercaptoethanol (ME) for short periods initiated at different times after fertilization. In both the first and second cleavage cycles, there was a phase during which cleavage delay increased linearly. This linear delay phase reflects the constant period of recovery from damage caused by ME treatment. The ME sensitive event is estimated to be present only briefly (about 5 minutes) immediately prior to the metaphase and appears to be associated with processes that determine the cleavage furrow. This ME sensitive event must develop only after completion of the puromycin sensitive event (protein synthesis required for division), because there is an exact correlation between the puromycin induced delay and delay in the appearance of the linear delay phase.

Lytechinus eggs treated briefly with ME before the first cleavage underwent quadripartition well before the second cleavage of controls. ME, therefore, appears to cause a premature splitting of centrioles prior to their duplication. Quadripartition can also be induced in androgenic merogones, verifying the old concept concerning the role of sperm centrioles in normal cleavage.